R.E. Weiss

Optical characteristics of atmospheric aerosols

Techniques have been developed to make point measurements of particle size, chemical nature, scattering and absorption extinction coefficients. These measurements have been shown to be sufficient to describe the optical or visual effects of trace materials in urban or rural air. These techniques and methods of analysis are described in this document. Conclusions include: scattering extinction and fine particle mass, absorption extinction and graphitic carbon are highly correlated. SO2−4 is usually the dominant scattering species and it occurs both in acid and neutral salt (with NH+4) forms. The role of organic carbon, especially in rural atmospheres appears small.

Particulate air pollutants: A comparison of British “Smoke” with optical absorption coefficient and elemental carbon concentration

Abstract Atmospheric aerosol samples collected simultaneously on four different filter media support the hypothesis that reflectance, as measured by the British “Smoke” method, is controlled by the optical absorption coefficient of the aerosol. An additional comparison shows that the British “Smoke” measure may be used to estimate concentrations of sub-μm, particulate, elemental carbon. Poorer correlations are suggested for the mass concentration of the particles suspended in air.

Sulfate Aerosol: Its Geographical Extent in the Midwestern and Southern United States

Sulfate particles (sulfuric acid and its neutralization products with ammonia) dominate the submicrometer-sized, light-scattering component of the aerosol in more than 90 percent of 2850 pairs of humidographic measurements made over a 3-month period at three rural midwestern and southern sites. The nearly continuous optical dominance by sulfate in the aerosol at these spatially varied locations, particularly in the Ozark Mountains, suggests that sulfate is a component of the submicrometer-sized aerosol that is distributed over a large geographical region and is not due to local sources.

Chemical speciation of H2S04—(NH4)2S04 particles using temperature and humidity controlled nephelometry☆

Abstract Measurment of the response of sulfate compounds in aerosol particles tp thermal decomposition at specific relative humidities providies semiquantitative chemical analysis for sulfate compounds and ammonium to sulfate molar ratio. Laborotory data are presented and discussed . Experiments at one Eastern U.S. site show ambient aerosol NH4+/SO4= between 0.5 and 2.0.

In-situ, rapid response measurement of H2SO4/(NH4)2SO4 aerosols in urban Houston: a comparison with rural Virginia

Abstract We report measurements taken in Houston, Texas of the chemical composition and degree of hydration of haze particles and compare these results with previously reported measurements taken in rural Virginia. Our in-situ, real time measurements are based on detecting changes in particle light scattering extinction with changes in relative humidity and air temperature. With these methods we can determine fine particle mass and sulfate mass concentrations, and sulfate to ammonium ion molar ratio. In Houston, fine particle sulfate averaged 42 % of fine particle mass and the composition in terms of ammonium to sulfate molar ratio ranged from 0.5 to 2 with strong diurnal variation. The particles were most acid during the period 1500 to 2000 and neutral during 0200 to 0900. About 1 3 of the time the particles were droplets supersaturated in terms of salt content. In Virginia, the particles were on average more acidic and contained more water than those in Houston, but the particles were never observed to be supersaturated solution droplets. The difference in the hygroscopic behavior of the particles at the two sites is consistent with differences in both particle chemistry and ambient relative humidity.

The color of denver haze

Abstract Objects change in color and brightness when viewed through polluted air and a haze layer itself has a color and brightness. The color of urban haze, often termed ‘brown’, was originally ascribed to the blue-absorbing gas, nitrogen dioxide (Hodkinson, 1966; Horvath, 1971,1972). More recently, others have shown that a brown coloration of haze can result from either particles or NO 2 , or a combination and each case must be considered in detail (Charlson and Ahlquist, 1971; Waggoner and Charlson, 1971; Husar and White, 1976; White and Patterson, 1981; Vanderpol and Humbert, 1981). We are describing teleradiometer measurements in which the haze color and brightness were determined to estimate the relative importance of particle and NO 2 optical extinction to the appearance of winter haze in Denver. During this program in November and December of 1978, we found that the haze was gray, not brown and aerosol particles were more effective than NO 2 in determining haze color and reduced visual range. Our measurements are consistent with coloration calculated from particle extinction and NO 2 concentration measurements.